Interpretive Summary: The sudden oak death pathogen, Phytophthora ramorum, is present in the United States as three clonal lineages. Hypervariable genetic markers, such as microsatellites, have been very useful for studying the movement of the clonal lineages and changes in the lineages over time. This study reports the results of screening 159 additional microsatellites for variation in the NA1 and NA2 clonal lineages. These markers have previously been screened in the EU1 clonal lineage. Five microsatellites were found to be variable in the NA1 lineage and one in the NA2 lineage. These markers will enhance future studies of genetic variation in P. ramorum populations.

Technical Abstract:
Phytophthora ramorum is a recently introduced pathogen consisting of three clonal lineages. Due to the very limited intra-lineage genetic variation, only a few polymorphic markers are available for use in studies involving the epidemiology and evolution of P. ramorum. A total of 159 primer pairs for candidate polymorphic SSR loci were tested with universal labeling. Five polymorphic microsatellite loci were identified within the NA1 lineage and one within the NA2 lineage, demonstrating the power and flexibility of the screening technique. The markers can significantly increase the number of genotypes that can be identified, and as such can help characterize the North American lineages of P. ramorum.